The present invention relates to metal billets, slabs, rods, and sputter targets. More particularly, the present invention relates to a method of producing a valve metal having a uniform fine grain size and a homogeneous microstructure that has dimensions sufficient for dividing into multiple slabs or billets for use in sputter targets and other objects.
Certain observable properties of sputter targets and sputter target materials are desirable for enhancing the sputtering performance of valve metal sputter targets (See, e.g., Michaluk, “Correlating Discrete Orientation and Grain Size to the Sputter Deposition Properties of Tantalum,” JEM, January, 2000; Michaluk, Smathers, and Field, Twelfth International Conference on Texture of Materials, J. A. Szpunar (ed.), National Research Council of Canada, 1999, p. 1357). Fine grain size and homogeneous microstructure that is substantially free of sharp texture bands are examples of such properties. Grain size, grain uniformity, and textural homogeneity of metal material, generally, and of target material in particular, are measurable qualities, by methods described, for example, in U.S. Pat. No. 6,462,339 B1 (Michaluk et al.), incorporated herein in its entirety by reference.
Hence, an ongoing interest exists in relevant markets to develop processes for producing high purity sputter targets having the above-described metallurgical and textural qualities. Conventional metalworking multi-step sequences incorporating forging and/or rolling steps, combined with one or more intermediate annealing steps as well as one or more cleaning steps, are typically used in manufacturing suitable mill forms and are generally described by C. Pokross, “Controlling the Texture of Tantalum Plate,” Journal of Metals, October 1989, pp. 46–49; and J. B. Clark, R. K. Garrett, Jr., T. L. Jungling, R. I. Asfahani, “Influence of Transverse Rolling on the Microstructural and Textural Development in Pure Tantalum,” Metallurgical Transactions A, 23A, pp. 2183–91, which are incorporated herein in their entirety by reference. An example of a multi-step forging, cleaning, annealing, and rolling process to produce a tantalum sputter target having fine grain size and a homogeneous texture is described in U.S. Pat. No. 6,348,113 (Michaluk et al.), incorporated herein in its entirety by reference.
At least one disadvantage of conventional sputter target manufacturing methods is a limited yield of sputter targets per product lot. Limited-quantity production of sputter targets has at least two drawbacks. First, it can be quite time-consuming and costly. That is, as shown in the present invention, target manufacturing efficiency can be achieved by simultaneous target material production, as well as by formation of oversized target-grade plates suitable for bonding to a backing plate and subsequent partitioning into multiple sputtering target assemblies. Another drawback concerns quality control. Variables in metalworking operations affecting target material properties can lead to variation in the metallurgical and textural qualities of serially produced sputter targets.
Accordingly, a need exists for a method to produce a sputter target material having superior metallurgical and textural qualities, and to reduce the costs associated with production of sputter targets exhibiting such qualities.